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The Hive => Chemistry Discourse => Topic started by: ChemicalSolution on December 22, 2001, 04:42:00 PM

Title: Ac2O synthesis idea
Post by: ChemicalSolution on December 22, 2001, 04:42:00 PM
GAA--> ac2O + H2O with heating however this is an equilibrium process and consequently we cannot heat GAA to 140 and distill it over as ac2O.

How about dripping GAA onto concentrated H2SO4?  One would think that the H2SO4 would dehydrate the GAA and form the anhydride.  This dream would probably start out by cooling 1.1 moles of H2SO4 on an ice bath and then dripping 1 mole GAA  onto the H2SO4 then heating until distillation.

Does anyone think this would work?--CH
Title: Study More Chemistry!!!
Post by: lugh on December 22, 2001, 06:13:00 PM

One would think that the H2SO4 would dehydrate the GAA and form the anhydride.



Perhaps "one" should think this over again, sulfuric acid doesn't cause the formation of anhydrides. It's the agent used to dehydrate aqueous acetic acid making glacial acetic acid.

Title: Re: Study More Chemistry!!!
Post by: ChemicalSolution on December 23, 2001, 07:00:00 AM
What about heating GAA with phthalic anhydride?  There has to be a way besides working through acetyl chloride.
Title: Re: Study More Chemistry!!!
Post by: terbium on December 23, 2001, 07:15:00 AM
There has to be a way besides working through acetyl chloride.
There is. It is called ketene.
Title: Re: Study More Chemistry!!!
Post by: uemura on December 23, 2001, 09:03:00 AM
Uemura would try P2O5 instead of phthalic anhydride:
x GAA +  y P2O5 -> z Ac2O + Phosphour acid
Merry XMas to the Bees
Title: Re: Study More Chemistry!!!
Post by: ChemicalSolution on December 25, 2001, 07:03:00 AM
Would phthalic anhydride work though?  It is MUCH cheaper for SWIM.  Besides, it can be re-generated.

Lets say someone did a batch with 1mole GAA and, say, 1.2 mole phthalic anhydride.  The ac2O is distilled over and what's left in the flask is heated to 200C to melt.  This will free H20 and regenerate the anhydride.

But really, back to the original question.  What would happen if you refluxed GAA with H2SO4?  We already know that GAA heated forms acO2 and H2O.  Would the water NOT ionize with the H2SO4 present, shifting the equalibrium toward anhydride synthesis?